Deep-submicron complementary metal oxide semiconductor (CMOS) is conventionally the primary technology for ultra-large scale integrated (ULSI) circuits. Over the last two decades, reduction in the size of CMOS transistors has been a principal focus of the microelectronics industry.
Transistors (e.g., MOSFETs), are often built on the top surface of a bulk substrate. The substrate is doped to form source and drain regions, and a conductive layer is provided between the source and drain regions. The conductive layer operates as a gate for the transistor; the gate controls current in a channel between the source and the drain regions.
Ultra-large-scale integrated (ULSI) circuits generally include a multitude of transistors, such as, more than one million transistors and even several million transistors that cooperate to perform various functions for an electronic component. The transistors are generally complementary metal oxide semiconductor field effect transistors (CMOSFETs) which include a gate conductor disposed between a source region and a drain region. The gate conductor is provided over a thin gate oxide material. Generally, the gate conductor can be a metal, a polysilicon, or polysilicon/germanium (SixGe(1.x)) material that controls charge carriers in a channel region between the drain and the source to turn the transistor on and off. Conventional processes typically utilize polysilicon based gate conductors because metal gate conductors are difficult to etch, are less compatible with front-end processing, and have relatively low melting points. The transistors can be N-channel MOSFETs or P-channel MOSFETs.
Generally, it is desirable to manufacture smaller transistors to increase the component density on an integrated circuit. It is also desirable to reduce the size of integrated circuit structures, such as vias, conductive lines, capacitors, resistors, isolation structures, contacts, interconnects, etc. For example, manufacturing a transistor having a reduced gate length (a reduced width of the gate conductor) can have significant benefits. Gate conductors with reduced widths can be formed more closely together, thereby increasing the transistor density on the IC. Further, gate conductors with reduced widths allow smaller transistors to be designed, thereby increasing speed and reducing power requirements for the transistors.
As critical dimensions (CDs) of device structures are made smaller, certain issues must be addressed during processing. One such issue involves the use of a wet etch to remove mask layers used in the formation of the structures. When structures having small critical dimensions are produced, the introduction of phosphoric acid or other aqueous etchants to remove a mask layer may damage the structure formed during the etching process.
Another issue involves the ability to form masks at very small sizes (e.g., 60 nanometers or less). For example, where a mask is formed by depositing a layer of material and removing a portion of the layer of material, it is difficult to reliably achieve a mask shape that has the desired dimensions. For example, etchants used to form the mask may cause the mask to collapse.
Thus, there is a need to form structures in an integrated circuit using an improved method that produces structures having reduced critical dimensions. Further, there is a need to produce structures that have reduced critical dimensions without damaging the structures during etching or processing of other layers. Even further, there is a need to use amorphous carbon as a mask in the formation of integrated circuit structures. Even further still, there is a need to form masks for producing features having small critical dimensions that maintain a desired shape during processing.